High frequency transmission system



A ril 23, 1935'. 1. J; KAAR HIGH FREQUENCY TRANSMISSION SYSTEM.

Filed Dec. 22,1950 I Inventor v Ira J. Kaar,

QWQAZQ His Attci neg.

Patented Apr. 23, 1935 1,998,960 HIGH FREQUENCY TRANSMISSION SYSTEM IraJ. Kaar, Schenectady, eral Electric Company,

York

N. Y., assignor to Gena corporation of New I Application December 22,1930, Serial No; 503,866

, V 11 Claims. My inventionrelates to high frequency transmissionsystems and more particularly to transmission lines for use intransmitting energy between a high frequency source and a radiatingsystem, or other load circuit.

Where transmission lines of considerable length are employed to supplyenergy from a source to a radiating system it frequently occurs thatconsiderable radiation of energy takes place from the transmission lineitself. This radiation' has been found to be due largely to currentsupon the line conductors of thefltransmission line having frequenciescorresponding to certain harmonics of the fundamental frequency which itis desired to transmit through the line. Currents of the fundamentalfrequency, of course, flow in opposite directions in the two lineconductors and therefore produce little or no radiation, but it has beenfound that currents: having one or more frequencies corresponding tocertain harmonics of the fundamentals, and which are excited in the linedue to inherent characteristics of thecoupling arrangements employed,flow in the same direction in the two line conductors; i. e. the twocon-.

ductors oscillate in phase with respect to ground thereby causingundesired radiation'into' space.

One of the objects of my invention is toreduce undesired harmonicradiation into space from the conductors-of the transmission line.

A further object of the inventior'iis to' provide a path for thecurrents which produce uncle sired radiation whereby said currents'flowin I opposite directions in adjacent conductors: thereby to causeneutralization of radiation from the conductors.

.A further object of the invention is to provide means whereby theeffective height of the transmission line conductors considered'as aradiator above ground is substantially reduced.

Still a further object of the invention is to: reduce reflected orstanding waves of the un-' desired harmonic frequency onthe line.

The novel features which Ibelieve to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which Figs. 1, 2 3 and 4 representdifferent embodiments of my invention.

Referring to Fig. I of the drawing, I'have represented by means of arectangule i any suitable equipment whereby high frequency oscillationsof suitable power are generated and supplied through a transformer '2,transmission line 3 and transformer 4' to a suitable load circuit whichmay comprise a radiating system 5, th radiating system being arranged atsome distance from the generating equipment I. The transmission line 3is so designed that it efficiently transmits energy of the fundamentalfrequency which is to be radiated from the source to the antenna. Tothis end condensers 6 are connected in series across the line inparallel with the primary winding of the transformer 4, these condenserstogether with the inductance of the transformer 4, and antennaresistance and'capacitance being of such value thatthe line isterminated in an impedance which is equal to the surge impedance of theline. Because of the impedance of the antenna which is reflected backintothe circuit of the primary winding of the transformer 4', thecondensers 6 must be of such value that the circuit com-, prising thecondensers and the primary winding of the transformer are slightly offresonance but such that the power factor of currents flowing from theline into the circuit comprising condensers 6 and the primary winding ofthe transformer 4 is unity Atthe opposite end of the line condensers lare connected in series with the secondary winding of the transformer 2,these condensers being of such value as to exactly neutralize theinductance of the secondary ,windingof .the transformer 2 whereby theentire in duced. electromotive force in the secondary winding ofthetransformer 2: transmission line.

It will be apparent from an inspection of the arrangement as thusdescribed that currents which are supplied to the transmission linethrough the inductive action'of the transformer 2 flow in oppositedirections in the two line conductors of the; transmission line, theenergy of these'currents being transmitted to the load circuit throughthe inductive. action of the transformer 4'. w i

It frequently occurs, however, that due to the inherent nature of thesource and the coupling arrangements: employed whereby energy issuppliedto. the transmission line that oscillations having frequenciescorrespondingto certain of the harmonics of the fundamental wave whichit is desired to transmit throughv the line flow in the same directionin the two line conductors. Thus, for examplaoassume that the sourceofoscillations t includes an electron discharge amplifier of the push:pull type of which the discharge devices are indicated at 8, the priisimpressed upon the mary' winding of the transformer 2 being connectedbetweenthe two. anodes of the push pull circuit and the midpoint thereofbeing connected through the common portion. of the output circuit tothe'cathodes of the discharge device. In this type of circuit currentimpulsesv flow alternately to the two anodes of the discharge devices.Since that portion of the circuit, however, which is between thecathodes and the intermediate point on the primary winding of thetransformer is common to the anode circuits of the two dischargedevices, it is apparent that a certain voltage will be built up acrossthis common portion of the circuit having a frequency corresponding tothe second and other even harmonics of the fundamental wave. Since thecathodes are grounded the entire primary winding oscillates with respectto ground at these even harmonics. Due to the capacity effect betweenthe primary and secondary windings these even harmonics are supplied tothe transmission line conductors in phase causing these conductors tooscillate in phase with respect to ground. While I mention a source ofoscillations including a push pull amplifier in the output stage in theway of illustrating one manner in which the harmonic oscillations aresupplied to the two conductors of the transmission line in phase, itwill be understood that I do not wish to be limited thereto since myinvention also has application in connection with sources of othertypes.

Normally the conductors of the transmission line are arranged at aconsiderable distance above the earth, thereby to avoid the effects ofsnow and ice upon the ground, and for other purposes. As such the linehas considerable effective height above ground when considered as aradiator of these harmonic frequency oscillations.

To avoid the effects of this radiation, in accordance with my presentinvention, a third conductor 9 is arranged symmetrically between the twoline conductors 3 and in proximity thereto. This conductor is connectedto the transmission line at a point between the condensers 6 at the loadend of the line and'is grounded at a number of different points alongthe line. In this way the conductors 3 are brought effectively closer toground and the effective height thereof when considered as a radiator ofthe harmonic frequencies is materially reduced, thereby substantiallyreducing the radiation into space.

It will be seen further that currents of the harmonic frequency whichflow in phase in the conductors 3 find a return path through theconductor 9 and flow in'this conductor in opposite direction to thecurrent of the same frequency in the conductors 3. Near the load end ofthe line these currents in the conductor 9 are substantially equal tothe sum of the currents of the same frequency in the conductors 3, andaccordingly any radiation from the two conductors is substantiallyneutralized. Of course a cer tain' amount of the return current is ledto ground through the successive ground connections Iii and accordinglythe neutralization is gradually less effective at points along the lineincreasingly remote from the antenna 5 but at all points 'ofthe line theconductor 9 is equally effective in reducing the effective height of thetransmission line. a

In Fig. 2 I have shown a further arrangement which may be employed. Inthis figure the point between the condenser E at the load end of theline is connected to ground through an impedance H equal to the surgeimpedance of the path through which the undesired harmonic frequenciesflow namely, the two conductors 3 in parallel. This arrangement isdisclosed and claimed in a copending application of John W. Labus.Serial No. 503,867 entitled High frequency circuits and filedsimultaneously herewith and which is assigned to the same assignee as mypresent application, The purpose of this impedance is to preventreflection of currents of the undesired harmonic frequencies from theend of the line remote from the transmitter thereby avoiding anystanding waves upon the transmission line conductors. This arrangementmay be made more effective by connecting a simi lar impedance I 2between the opposite end of the line and ground, these two impedancesthus serving each to prevent reflection from its respective end of theline of currents received from the opposite end of the line. Thus ifreflection occurs at the load end of theline the reflected currents areprevented by the impedance l2 from being again reflected at thetransmitting end of the line.

In Fig. 3 I have shown an arrangement in which the advantages of bothFigs. 1 and 2 may be secured, the conductor 9 being connected betweenthe impedances H and I2 and arranged symmetrically in proximity to theconductors 3, this conductor being grounded at the opposite endsthereof, and at additional points, if desired. As such the conductorserves both to reduce the effective height of the line conductor 3 andalso to neutralize the radiation therefrom.

Fig. 4 shows a further arrangementin which the conductor 9 is connectedto the transmission line at a point between the condensers 6 and isextended symmetrically throughout the length of the line in proximity tothe conductors 3 and is there connected to ground through an impedancewhich is equal to the surge impedance of the line, the two conductorsthereof being considered as connected in parallel-and the conduc tor 9serving as a return path. In this arrangement it will be seen that thecurrents flowing in the same direction in the conductors 3 find a returnpath through the conductor 9 and substantially neutralize the field ofconductors 3 throughout the entire length of the line and the impedanceI I prevents standing waves upon the line.

While I have shown particular embodiments of my invention, it will ofcourse be understood that I do not wish to be limited thereto sincedifierent modifications may be made, and that I contemplate bytheappended claims to cover any such modifications as fall within thetrue spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a source of high frequency oscillations of a certainfundamental frequency, a radiating antenna, a transmission linecomprising line conductors connected between said source of highfrequency oscillations and said radiating antenna to carry currents ofsaid fundamental frequency in opposite directions, and means to reduceradiation of energy from said transmission line due to currents flowingin the same direction in the two conductors of said line, said meanscomprising a third conductor extending symmetrically between saidconductors in proximity to said two line conductors and arranged tocarry in the opposite direction currents which flow in' said two lineconductors in the same direction whereby radiation from said two lineconductors is neutralized by radiation from said third conductor.

2. In combination, a source of high frequency oscillations of a certainfundamental frequency,- a radiating antenna, a transmission line com=prising line conductors connected between said source of high frequencyoscillation and said radiating antenna to carry currents of saidfundamental frequency in opposite directions, and means to reduceradiation of energy from said transmission line due to currents flowingin the same direction in the two conductors of said line said meanscomprising a third conductor extending along said line in proximity tosaid two line conductors and arranged to carry in the opposite directioncurrents which flow in said two line conductors in the same direction,whereby radiation from said two line conductors is neutralized byradiation from said third conductor and an impedance connected in saidthird conductor having a value equal to the surge impedance of the paththrough which said currents flow.

3. In combination, a source of high frequency oscillations of a certainfundamental frequency, a radiating antenna, a transmission linecomprising line conductors connected between said source of highfrequency oscillations and said radiating antenna to carry currents ofsaid fundamental frequency in opposite directions, and means to reduceradiation of energy from said transmission line due to currents flowingin the same direction in the two conductors of said line having afrequency which is a harmonic of said fundamental frequency, said meanscomprising an impedance connected between each end of said line andground, each of said impedances having a value to prevent reflection atthe respective end of the line of currents of said harmonic frequencyreceived from the opposite end of the line and flowing in the samedirection in said two line conductors.

4. In combination, a source of high frequency oscillations of a certainfundamental frequency, a radiating antenna, a transmission linecomprising line conductors connected between said source of highfrequency oscillations and said radiating antenna to carry currents ofsaid fundamental frequency in opposite directions, and means to reduceradiation of energy from said transmission line due to currents flowingin the same direc- 7 tion in the two conductors of said line, said meanscomprising an impedance connected between each end of said line andground, each of said impedances having a value to prevent reflection atthe respective end of the line of currents received from the oppositeend of the line and flowing in the same direction in said two lineconductors and a third conductor connected between said two impedancesand arranged in proximity to said two line conductors.

5. In combination, a source of high frequency oscillations of a certainfundamental frequency, a radiating antenna, a transmission linecomprising line conductors connected between said source of highfrequency oscillations and said radiating antenna to carry currents ofsaid fundamental frequency in opposite directions, and means to reduceradiation of energy from said transmission line due to currents flowingin the same direction in the two conductors of said line said meanscomprising a third conductor eX- tending along said line in proximity tosaid two line conductors and arranged to carry in the opposite directioncurrents which flow in said twoline conductors in the same directionwhereby radiation from said two line conductors is neutralized byradiation from said third conductor and a plurality of connections fromsaid third conductor to ground said connections being disposed atdifferent points along the line.

6. In combination, a source of high frequency oscillations of a certainfundamental frequency, a load circuit, a transmission line arranged totransmit oscillations of said fundamental frequency from said source tosaid load circuit, said transmission line comprising a pair of lineconductors, and a coupling between said source and said transmissionline whereby current of said fundamental frequency is caused to flowin'opposite directions in said line and currents having the frequency ofcertain harmonics of said fundamental frequency are caused to flow inthe same direction in said line, said line conductors being arrangedabove the ground at a distance to produce undesired radiation intospace, and a third conductor arranged in proximity to said lineconductors and connected in circuit relation with said line conductorswith respect to said certain harmonics of said fundamental, and meansfor maintaining said third conductor substantially at ground potentialthereby to reduce the effective height of said line conductors.

7. A method of reducing radiation of undesired harmonic energy from anunshielded transmission line elevated above the earth and isolated fromgrounded conducting objects, the two sides of'said transmission lineconducting desired currents in opposite phase and an undesired harmonicthereof in like phase, which includes the step of reducing the effectiveheight of the transmission line above the earth for said undesiredharmonic currents flowing in phase in the opposite sides of saidtransmission line, while maintaining the actual height of saidtransmission line.

8. The method of reducing undesired harmonic radiation of energy from anunshielded transmission line elevated above the earth and isolated fromgrounded conducting objects which includes producing a field of groundpotential at the undesired harmonic frequency in proximity to asubstantial portion of the transmission line.

9. In a system for transmitting high frequency energy from a source to aload comprising a transmission line connected between said source andload, the method of reducing radiation from said line produced bycurrents flowing in the same direction in opposite sides of said linehaving a frequency which is a harmonic of the frequency to betransmitted over said line, which includes neutralizing the field inspace produced by said harmonic currents.

V 10. In a system for transmitting high frequency energy from a sourceto a load comprising a transmission line, connected between said sourceand load, the method of reducing radiation from said line produced bycurrents flowing in the same direction in opposite sides of said line,which includes transmitting said currents in the opposite directionalong said line thereby toproduce a field in space opposing the fieldproduced by currents in said opposite sides of said line.

11. In a system for transmitting high frequency energy from a source toa load comprising a transmission line connected between said source andload, the method of reducing radiation from said line produced bycurrents flowing in the same direction in opposite sides of said line inwhich desired currents flow in opposite directions, which includesneutralizing the field in space produced by said currents and reducingthe effective height of the transmission line above the earth whilemaintaining its actual height.

IRA J. KAAR.

